fix building on GNU Hurd

apps/openmw/crashcatcher.cpp

@@ -37,6 +37,10 @@ static const char pipe_err[] = "!!! Failed to create pipe\n";
 static const char fork_err[] = "!!! Failed to fork debug process\n";
 static const char exec_err[] = "!!! Failed to exec debug process\n";
 
+#ifndef PATH_MAX		/* Not all platforms (GNU Hurd) have this. */
+#	define PATH_MAX 256
+#endif
+
 static char argv0[PATH_MAX];
 
 static char altstack[SIGSTKSZ];